Hardness Prediction of Copper Wire Produced by Continuous Equal Channel Angular Extrusion

• Main Authors: KAO, CHUN-HSUAN, 高群軒
• Other Authors: CHANG, CHAO-CHENG
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/ftvyun

碩士 === 國立高雄科技大學 === 模具工程系 === 107 === Hardness is generally defined as resistance to permanent indentation on a surface of solid material. It is one of important properties to indicate the strength of metals. However, the traditional hardness test is not only time-consuming to undertake, but also produces the indentation of plastic deformation on the surface of the specimen. Therefore, how to establish a reliable hardness prediction method is one of current research topics of interests. This study developed two models for hardness prediction which are the curve of the relationship between strain and hardness and the curve of the relationship between strain and grain size. The models were then used to estimate the harness of the copper wire processed by a continuous equal channel angular extrusion. In this study, the copper wire with 1 mm diameter was machined and ground as specimens with 1.5 mm height for simple compression tests in which the specimens were compressed up to 70 % by an increment of 10% of height reduction. The compressed specimens were then prepared for metallographic observation and Vickers microhardness tests. Moreover, the equivalent strains of the compression tests were also predicted by a finite element software. With the data of the measured hardness and predicted strain, the curve of the relationship between strain and hardness was established. In addition, considering the change in grain size due to plastic deformation, the study also constructed the curve of the relationship between grain size and hardness. Furthermore, this study conducted the experiments of continuous equal channel angular extrusion for the copper wire with 1 mm diameter. The process was also simulated by a simplified numerical model in order to reduce the computing time. Finally, the predicted strain and measured grain size were separately used in two models of hardness prediction and hardness tests were performed to verify the accuracy of the models. The results show that the curve of the relationship between strain and hardness is able to estimate the hardness variation close to the measured one in the copper wire processed by the continuous equal channel angular extrusion, and the maximum difference between the prediction and measurement is about 30%. Moreover, the curve of the relationship between grain size and hardness gives more accurate predictions than those predicted by the curve of the relationship between strain and hardness, and the maximum difference is about 18%. Keywords: Metal Forming, Continuous Equal Channel Angular Extrusion, Hardness Prediction